Increased concern about the environment, especially the quality and condition of water in rivers, lakes and canals, has raised a general requirement for monitoring and measuring parameters relating to water to a much greater extent than hitherto. Due to practical limitations, sampling and testing of water has generally been done manually at only a few locations and with limited frequency. Part of the difficulty is that testing sites are often at inconvenient and remote places. While yielding only inadequate amounts of information, this process is very expensive in time, travel costs and labour, and cannot economically be extended to achieve the very much larger number of monitoring points and sampling frequencies required for enabling quick remedial action to counter pollution sources.
Automatic monitoring and measuring devices have been deployed recently in rivers, lakes and canals to increase the frequency of sampling. Commonly called sondes, these sensors measure a large number of possible different parameters relating to the condition of the water. Measurements typically include but are not limited to aspects such as: flow rate; water depth by pressure sensing; water depth by ultrasonic techniques; temperature; acidity/alkalinity (pH); conductivity; dissolved oxygen content; chlorophyll density; salinity and presence of chemicals such as ammonium salts and nitrates; presence of other specific pollutants determined by chemical analysis sensors; presence of blue-green and other potentially toxic algae; particulate content, and turbidity.
Typically, automatic sondes are raised manually from a river or lakebed by personnel on a boat and their data is downloaded to a data-storage device before being transported physically back to a laboratory or data centre. Usually, the position of each sonde is marked, for example, using a buoy or other marker. Sometimes, the sonde is physically connected to the buoy. In this case, the buoy can be arranged to contain a repeater station for taking data from the underwater sonde and transmitting it onwards by conventional short-range radio to a land station. Unfortunately, the presence of a buoy is undesirable because it can draw unwanted attention, with high probability of damage and theft of the equipment. Moreover, in places of natural beauty a visible buoy may be considered unacceptable. A buoy also may preclude the positioning of a sonde in places where there is passing water traffic, such as the middle of a canal which might otherwise be an optimal location.
In a few cases, sondes are connected by cable laid along the river or lake bottom to a node in an equipment cabinet on dry land near the bank, whence conventional communication methods are used to transmit results to a data centre in real-time. While accomplishing the goal of frequent results nearly in real-time, such a direct cable connection is not an ideal solution to the local communication problem. A cable laid along the bottom is expensive to install in a manner that will avoid accidental damage by watercourse users, maintenance operations and floods, and remain hidden for security reasons. It will usually require planning permission and is likely to require a trench in both its underwater and on-shore sections. Once a cable is deployed, repositioning of the sonde then becomes prohibitively difficult.